Given below are two statements: one is labelled as Assertion (A)...

The radius of a nucleus is given by $R = R_0 A^{1/3}$.
The volume of the nucleus is $V = \dfrac{4}{3}\pi R^3 = \dfrac{4}{3}\pi R_0^3 A$.
The mass of the nucleus is approximately $mA$, where $m$ is the average mass of a nucleon.
Nuclear density $\rho = \dfrac{\text{Mass}}{\text{Volume}} = \dfrac{mA}{\dfrac{4}{3}\pi R_0^3 A} = \dfrac{3m}{4\pi R_0^3}$.
Since $m$ and $R_0$ are constants, the nuclear density is independent of the mass number $A$. Thus, Assertion (A) is true.

The strong nuclear force is a short-range force (acting effectively only over distances of a few femtometers) and exhibits a saturation effect, meaning a nucleon interacts strongly only with its nearest neighbours. This saturation is the underlying reason for the constancy of binding energy per nucleon and nuclear density. Thus, Reason (R) is false.

Answer: Assertion (A) is true but Reason (R) is false.